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Author Topic:   Valve reliefs
Mikey14
Member
posted March 19, 2004 12:10 PM
How much volume is in most valve reliefs? I've got 64cc heads with speedpro hypers that have 4 valve releifs in em. I was guessing at 4cc's per piston additional volume. I'm just trying to get close on our compression ratio as the difference between 64 and 68cc's is a ton of difference in compression.

I'm trying to get close using the compression formula in the tool box.

Thanks,

goinrcn44h
Member
posted March 19, 2004 12:26 PM
They should tell ya what the dome volume is in cc's somewhere, whether it be positive or negative. unless its something you had done by flycutting or something, then you would need to have that clear plastic unit for cc'ing domes and a syringe that has graduations in cc's on the side. pretty simple process really.

44H

sdhnc29
Member
posted March 19, 2004 01:37 PM
Generally on a 2 valve relief flat top, you'll gain 4-7 cc's in the valve pocket. This will depend on the depth of each pocket. I'm not sure on a 4 valve relief piston with concentric pockets.

Steve

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Mikey14
Member
posted March 23, 2004 08:46 AM
Thanks for the help. Guessing conservativly then if I add 7 cc's to the 4 valve piston I'll get 71cc total volume which puts me at 9.1 compression with a .038 gasket in a 355. I have to be under 9.3 so looks like I'm ok. Now if I wanted to push the envelop.....


stockcar5
Member
posted March 23, 2004 11:12 AM
the speed pros have a 5cc relief. you'll have 9.8 to 1 with a .038 head gasket and a standard deck height of .025. if your block was zero decked it'll be closer to 10.27 to 1. you'll probably need a thicker head gasket or different pistons.

luke

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Mikey14
Member
posted March 24, 2004 02:11 PM
ok,

I ran the numbers again through the toolbox utility with these numbers: 4.030 bore, 3.48 crank, 8 cylinders, 69 cc's (64 cc head plus 5 cc's) and got 9.38 which is "legal" at my track.

How'd you get such high ratio's? did you subtract the 5 cc's? I got 10.79 when I subtracted it. I know deck height matters but I'm just using the toolbox application to get a rough guide.

stockcar5
Member
posted March 24, 2004 04:46 PM
i put those numbers in the toolbox and came up with what you did..9.38.

i normally use the calulator at www.rosspistons.com or on speed pros website....and both of them give me 9.85 with the same figures. i have always thought the numbers from the calulator in the toolbox didnt seem right so i never use it.

luke

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jammin
Administrator
posted March 24, 2004 07:10 PM
Send me info if you see something is broken, I will get it fixed....found the problem.........should be fixed now...sorry bout that...It was a small problem with the volume of the head gasket, thats why it came out a bit low. Fixed now.

jam

[This message has been edited by jammin (edited March 26, 2004).]

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